SINTERED FE{13 CR{13 C{13 {8 MO{13 V{13 Ni{9 {11 ALLOYS IMPREGNATED WITH Pb OR Rb-BASE ALLOYS

ABSTRACT

A lead-filled sintered ferrous alloy containing carbon and chrome and preferably also molybdenum and vanadium is prepared in a powder metallurgy method and impregnated in its voids with lead. The alloy is characterized for its increased wear and heat resistant abilities and is accordingly advantageous when used as a material of a valve seat of an internal combustion engine using leadless fuel.

States Patent 1 Seino et a1.

[ May 28, 1974 ALLGYSTMFRTTCWKTEIYWTTE PB OR RB-BASE ALLOYS Inventors:Hiroshi Seino, Yokohama; Shingichi Suzuno, Tokyo; Yoshiaki Takeya,Matsudo; Tsutomu Tobita, Matsudo; Takeshi Fukaya, Matsudo, all of JapanAssignees: Nissan Motor Company, Ltd., Yokohama; Hitachi Powdered MetalsCompany, Matsudo, both of, Japan Filed: Dec. 19, 1972 Appl. No.: 316,545

Foreign Application Priority Data Dec. 27, 1971 Japan 46-105526 US. Cl.29/l82.l, 75/200 Int. Cl. B221 3/26, B22f 5/00, C22c 1/08 [58] Field ofSearch 29/1821; 75/200; 252/12 [56] References Cited UNITED STATESPATENTS 2,192,792 3/1940 Kurtz Q. 29/1821 X 2,409,307 10/ l 946 Patch.

2,561,579 7/1951 Lenel 29/1821 X 3,495,957 2/1970 Matoba e a1 29/1821Primary Examiner-Leland A. Sebastian Assistant ExaminerR. E. Sc'hafer [57] ABSTRACT 9 Claims, 5 Drawing Figures PATENYEMY 28 I974 3.812.565sumzura DPH NUMBER, 3009 LOAD 5 8 O 0 TEMPERATURE (C) TEMPERATURE we)PATENIEDMY 28 I9 4 3.812.585

sum 3 or 3 Fig. 5

E I 2 l E s v 1 i HEAT RESIST. L 0.6 STEEL, HNV-6 T T g ALLO: n g 0.2 O

TESTING HOURS SINTERED FEClR-C[M-VNI] ALLOYS IMPREGNATEID WITH PB ORRB-BASE ALLOYS The present invention relates to sintered ferrous alloysand, more particularly, to sintered ferrous alloys having wear and heatresistant properties. In spite of the fact that the sintered ferrousalloy herein disclosed will find a wide variety of practicalapplications for wear resistant and high-temperature services, it willbe described by way of example as specifically used as the material forvalve seats for automotive internal conbustion engines in which thevalve seats are subject to serious wear and elevated temperature duringoperation.

Fuel containing lead or a lead compound such as tetraethyl lead as oneof the typical chemical additives has long been employed for internalcombustion engines of motor vehicles or other vehicles except for marineuse. As is well known, the lead constituent in the automotive enginefuel is one of the major causes of vehicular air-pollution. To provideone solution to the problem, it is presently required to have such fuelsupplanted by leadless fuel such as leadless gasoline and liquefiedperoleum gas.

It is, however, pointed out that some barriers are encountered where theleadless fuel is combusted in the automotive engine. For one thing, thevalve seat which is formed for instance of heat-resistant cast irontends to be worn at its area to contact the valve face in a relativelyshort time to such an extent that'the valve is no longer properlyworkable. A search for a. material which is congruous for the valve seatof the internal combustion engine is thus currently subject of intensiveresearch and development in the automotive and allied industries.

An object of the present invention is, therefore, to provide a new anduseful material which is capable of withstanding wear and abrasion atelevated temperatures.

Another object of the invention is to provide a new and useful sinteredferrous alloy which is especially adapted for use as a material for avalve seat member of an automotive internal combustion engine.

Other objects and the nature and advantages of the sintered ferrousalloy provided in accordance with the present invention will becomeapparent from the following description of the invention when'taken inconjunction with the accompanying drawing in which:

FIG. I is a graph indicating a relationship between tensile strength andtemperature as exhibited in sintered ferrous alloys according to thepresent invention;

FIG. 2 is a graph indicating a relationship between hardness andproportion of chrome in a sintered ferrous alloy and a relationshipbetween tensile strength and proportion of chrome in the same alloy;

FIG. 3 is a graph illustrating variations in hardness against elevatedtemperature as observed in various metal materials including a sinteredferrous alloy proposed by the present invention;

FIG. 4 is a graph indicating a relationship between the coefficient oflinear expansion and temperature in various sintered ferrous alloysincluding those implementing the present invention; and

FIG. 5 is a graph showing the amounts of wear in terms of time in hoursof various metal materials including those which are provided inaccordance with the present invention.

Two different materials appeared as usable for building the valve seatmembers of the internal combustion engines which are well compatiblewith leadless fuels a sintered ferrous alloy having a lead constituentand a sintered ferrous alloy the voids of which are filled with lead.

According to the experiments we conducted, however, it has turned outthat the ferrous alloy of the kind which is prepared by compacting andsintering metal particles in the presence of lead has a wear-resistantproperty which is short of the acceptable level. This is consideredattributable to an insufficient mechanical strength of the base steeland to a limited proportion of the lead constituent in the ferrous alloyof the particular kind. The lead containing ferrous alloy produced inthe powder metallurgy method is thus unacceptable as the material forthe valve seat of the internal combustion engine using leadless fuel.

The sintered ferrous alloy filled with lead in its voids, on the otherhand, has proved to have a wear resistance of an acceptable order,according to other experiments conducted by us. Bench tests were furtherconducted in which the valve seat formed of the lead filled ferrousalloy was actually installed on an automotive internal combustionengine. The sintered ferrous alloy used in these tests contained, on aweight basis, 3 percent of copper, l.4percent of molybdenum, 0.9 percentof carbon and the balance iron. The tests revealed that a considerableamount of play is invited between the valve seat member and the enginecylinder head in which the valve seat member was shrink fitted as usual.Although the particular material may find extensive and successfulapplications in general wear resistant services, the material is notacceptable as the wear and heat resistant material for the valve seat ofthe internal combustion engine.

Researches were therefore further conducted in quest for the reasonsaccounting for the fact that the lead impregnated sintered ferrous alloyfails to exhibit the expected mechanical properties when used in theinternal combustion engines. Experiments were thus conducted withsintered ferrous alloys having and not having a lead filling therein forthe purpose of examining the variation in tensile strength of theseferrous alloys at elevated temperatures, the results being demonstratedby curves 0 and b in FIG. ll. The curve a represents the sinteredferrous alloy filled with lead while the curve b represents the sinteredferrous alloy which is similar in composition to the former but which isvoid of the lead filling.

It is quite apparent from these curves a and b that the tensile strengthof the lead filled ferrous alloy remains higher than that of theunfilled alloy within a temperature range from 50C to about 200C anddiminishes steeply as the temperature rises beyond the particular range.The curves also indicate that, when the lead filled ferrous alloy issubjected to a temperature higher than the melting point of lead whichis in the neighbourhood of 327C as shown in FIG. I, then the tensilestrength of the alloy becomes outstandingly lower than that oftheferrous alloy not filled with lead. Though not shown, it was alsoascertained that similar tendencies are exhibited in respect of theradial crushing strength of the alloys tested.

The valve seat member of the internal combustion engine usually has alimit in external size which is so prescribed that the seat member isinterference or shrink fitted into a mounting hole formed in thecylinder head. It therefore follows that the valve seat member issubjected to repeated expansion and contraction while being constantlyunder compression by the surrounding portion of the cylinder head, whichis different from the sliding parts. In order that the valve seat memberbe will give satisfactory service in the engine cylinder, it should beendowed with not only a wear resistance of a sufficient order but alsowith an increased fatigue property against thermal shock. With this inmind, it is herein pointed out that the problems have thus far beeninvolved in the prior art lead filled sintered ferrous alloys because ofthe fact that only those properties of the alloys which are displayed bythe base steel which is to be filled with lead have been taken intocomsideration.

The goal of the present invention is, thereforeato provide an improvedsintered ferrous alloy exhibiting sufficient wear resistance and fatigueproperty against thermal shock when used, for example, in the internalcombustion engine using leadless fuel. Such goal has been achieved byvirtue of intensive research and development covering a wide variety ofsintered steels.

It was found in the course of the research and development programs thatthe hardness of a sintered ferrous alloy containing chrome and 0.6 to1.2 percent by weight of carbon alloying elements increases as theproportion of the chrome constituent increases and that the tensilestrength of the alloy drops when the content of the chrome increasesbeyond 2.5 percent on a weight basis. This is graphically demonstratedin FIG. 2, in which the hardness of the alloy is indicated in termsofthe diamond pyramid hardness number (DPH) under a 300-gram load. FromFIG. 2, it is understood that both the hardness and tensile strength ofthe sintered ferrous alloy are acceptable where the alloy contains about2 to 3 percent of chrome.

The present invention thus proposes a new lead filled sintered ferrousalloy containing 0.6 to 1.2 percent of carbon, 2 to 4 percent of chromeand the remaining percentage ofiron on a weight basis. Experiments haverevealed that the ferrous alloy having this composition is advantageousfor use a material for the valve seats of internal combustion engineswhich are driven under relatively light loads. For the valve seats to beincorporated in engines driven under heavier load conditions, it ispreferable that the lead filled sintered ferrous alloys contain 0.6 to1.2 per cent of carbon, 2 to 4 percent of chrome, 0.2 to 0.5 percent ofmolybdenum, 0.2 to 0.4 percent of vanadium and the remaining percentageof iron, all on a weight basis.

To add to the toughness of the lead-filled sintered ferrous alloy, thealloy may further contain l to 4 percent of nickel. This will proveadvantageous where it is desired that the safety of operation of theengine be enhanced.

The lead with which the sintered ferrous alloy is filled may include notonly elemental lead but also a lead based alloy having a relatively lowmelting temperature and containing at least one of tin, antimony.cadmium and bismuth. Where the sintered ferrous alloy according to thepresent invention is used as the material for the valve seats ofinternal combustion engines, the alloy filled with elemental lead willbe suitable for engines driven at relatively high temperatures and thealloy filled with the lead alloy for engines driven at relatively lowtemperatures. Since, moreover, the proportion of the carbon in the alloyaccording to the present invention is limited to a range of 0.2 to 0.5percent by weight, the mechanical strength of the alloy remainssubstantially constant irrespective of a change in the proportion ofcarbon. This will provide ease of controlling the sintering operation ofthe alloy and accordingly a stabilized quality of the final product.

The sintered ferrous alloy to be filled with lead is usually fabricatedby the powder metallurgy method which in itself is well known in theart. In this instance, each of the constituents of the alloy may beprovided in the form of powder of the element or, for the prevention ofsegregation of the particles and to provide ease of quality control,each constituent may be provided in the form of an alloy powder. Thequantity of carbon, on the other hand, should be determined inconsideration of the hydrogen loss.

Since, moreover, the ferrous alloy according to the present inventioncontains chrome, it is important that the mixed powders of theconstituents be sintered in the presence of a highly reducing atmospherewith a relatively low humidity and at an elevated temperature.

The following table indicates compositions and mechanical properties ofa representative prior art sintered ferrous alloy which is denoted by Aand of the sintered ferrous alloys B, C and D which are prepared inaccordance with the present invention. The prior art ferrous alloy A isprepared from mixed powders of elemental carbon, molybdenum, copper andiron and sintered at a temperature of l,l30C for 30 minutes. Thesintered ferrous alloys B and C according to the present invention areprepared eachfrom a mixture of graphite powder and powders of alloyingelements and sintered in an atmosphere of refined hydrogen at atemperature of l,250C for 30 minutes.

Known Alloy Alloys of the Invention A B C Continued Known Alloy Alloysof the Invention A B C D The sintered ferrous alloy B is an example inwhich only carbon and chrome are used as the alloying elements while thesintered ferrous alloy C is an example containing molybdenum andvanadium in addition to carbon and chrome as the alloying elements. Thealloys A to C are all void of lead filling while the sintered ferrousalloy D is an example in which an alloy having thesame composition asthe alloy C has its pores filled with lead at a temperature of about1,000C. To ensure sufficient wear resistance property of the sinteredferrous alloy to be used as the material for the engine valve seats, itis important that the pores of the alloy be filled with at least percentby weight of lead.

Comparison between the mechanical properties of the sintered ferrousalloys B and C according to the present invention will reveal that themechanical properties are considerably improved through addition ofmolybdenum and vanadium as will be appreciated from the above presentedtable. It is, in this instance, preferable that the porportion ofmolybdenum is in the range of 0.2 to 0.5 percent by weight and theproportion of vanadium in the range of 0.2 to 0.4 percent by weight.Experiments have indicated that inclusion of these alloying elements ingreater or smaller proportions than indicated results in impairment ofthe mechanical properties of the resultant ferrous alloy.

Tests were further conducted so as to examine the variation in hardnessat elevated temperatures of the chrome containing, sintered ferrousalloy according to the present invention. The results of the tests onthe alloy C having the composition indicated in the previously presentedtable are illustrated in FIG. 3 in comparison with these of the testsconducted on the prior art sintered ferrous alloy A and a heat-resistantcast iron of the composition complying with SAE D-3. The cast iron thuscontains 2.2 percent of carbon, 0.35 percent of manganese, 2.6 percentof silicon, 3.4 percent ofchrome, 1.0 percent of molybdenum and theremaining percentage of iron and impurities, all on a weight basis. FromFIG. 3, it is quite apparent that the sintered ferrous alloy accordingto the present invention has peculiar properties as compared withthe twoprior art materials. While the hardnesses of the known sintered ferrousalloy and the specified heat-resistant cast iron diminish as they aresubjected to rising temperatures, the sintered ferrous alloy C accordingto the present invention exhibits a property such that the hardnessthereof increases as the temperature rises to the vicinity of 300C. Thehardness of the alloy C drops as the temperature rises beyond about 300Cbut still reamins at a level of the order of the hardness at a nonnaltemperature when heated up to the vicinity of 400C.

FIG. 4 illustrates curves indicating the variations of the coefficientsof linear expansion at elevated temperatures of the sintered ferrousalloy A of the prior art composition and the sintered ferrous alloys Cand D according to the present invention. These curves show that thecoefficients of linear expansion of the ferrous alloys C and D arelimited to relative low levels as compared with that of the prior artferrous alloy A. This means that, where the ferrous alloys C and D areused as the material for the valve seat members of the internalcombustion engines, the valve seat memebers are subjected tosignificantly reduced expansion and contraction when the engine is beingdriven. The increased hardness and reduced variation in the coefficientof linear expansion at elevated temperatures of the material accordingto the present invention will thus considerably contribute toimprovement of the heat-resistant ability and to prolongation of theservice life of the valve seat members formed of such material.

For the purpose of rating the wear resistance of the valve seat memberformed of the lead filled sintered ferrous alloy according to thepresent invention, bench tests were made on 1,800cc-capacityfour-cylinder internal combustion engines using valve seats formed ofthe lead impregnated and unimpregnated sintered ferrous alloys D and C,respectively, and two known materials for the sake of comparison. Theknown materials were heatresistant cast iron having the previously notedcomposition complying with SAE D-8 and heatresistant steel complyingwith SAE HNV-6, viz., con taining 0.80 percent of carbon, 0.40 percentof manganese, 2.30 percent of silicon, 20.00 percent of chrome, 1.30percent of nickel and the remaining percentage of iron, on a weightbasis. Every test was conducted for a continuous hour period on afull-load basis, wherein the acceptance level was prescribed at 0.3 mmwear. The results of these bench tests are illustrated in FIG. 5. Thesatisfactory wear resistance character of the lead-impregnated sinteredferrous alloy according to the present invention can be ascertained fromthe curves illustrated in FIG. 5. A bench test was also conducted on asimilar engine using valve seat members of a lead-filled sinteredferrous alloy having a composition similar to that of the sinteredferrous alloy B. The test revealed that the Wear resistance of suchmaterial is somewhat inferior to, yet roughly comparable to thatachieved by the sintered ferrous alloy C, though not shown in FIG. 5.

Tests were further made on motor vehicles in which the engine havingvalve seats of lead filled sintered ferrous alloy according to thepresent invention installed, and the vehicle driven a distance of 50,000kilometers with use of liquefied petroleum gas. It was clearlyascertained that the'lead filled sintered ferrous alloy according to thepresent invention is fully congruous for the valve seats of internalcombustion engines using leadless fuel.

What is claimed is:

l. A wear and heat resistant composition comprising a sintered ferrousbase alloy comprising 0.6 to 1.2 percent carbon by weight, 2 to 4percent chromium by weight, and the remainder iron, the pores of saidsintered ferrous base alloy being impregnated with a material selectedfrom the group consisting of lead and lead based alloys, the materialconstituting at least 10 percent by weight of the ferrous base alloy.

2. A composition as claimed in claim 1 wherein said impregnated materialis a lead based alloy containing at least one element selected from thegroup consisting of tin, antimony, cadmium and bismuth.

3. A composition as claimed in claim 1 wherein said impregnated materialis lead.

4. A composition as claimed in claim 1 wherein said sintered ferrousbase alloy further comprises 0.2 to 0.5 percent molybdenum by weight and0.2 to 0.4 percent vanadium by weight.

5. A composition as claimed in claim 4 wherein said impregnated materialis a lead based alloy containing at least one element selected from thegroup consisting

2. A composition as claimed in claim 1 wherein said impregnated materialis a lead based alloy containing at least one element selected from thegroup consisting of tin, antimony, cadmium and bismuth.
 3. A compositionas claimed in claim 1 wherein said impregnated material is lead.
 4. Acomposition as claimed in claim 1 wherein said sintered ferrous basealloy further comprises 0.2 to 0.5 percent molybdenum by weight and 0.2to 0.4 percent vanadium by weight.
 5. A composition as claimed in claim4 wherein said impregnated material is a lead based alloy containing atleast one element selected from the group consisting of tin, antimony,cadmium and bismuth.
 6. A composition as claimed in claim 4 wherein saidimpregnated material is lead.
 7. A composition as claimed in claim 4wherein said sintered ferrous base alloy further comprises 1 to 4percent nickel by weight.
 8. A composition as claimed in claim 7 whereinsaid impregnated material is a lead based alloy containing at least oneelement selected from the goup consisting of tin, antimony, cadmium andbismuth.
 9. A composition as claimed in claim 7 wherein said impregnatedmaterial is lead.